1. Field of the Invention
Embodiments of the present invention are generally related to a fiber assembly for all-fiber delivery of high energy femtosecond pulses. More specifically, embodiments of the present invention relate to a system and method for improving dispersion management when utilizing hollow core photonic bandgap fibers for pulse compression.
2. Description of the Related Art
Fiber optic delivery of femtosecond laser pulses is attractive for several reasons. An all-fiber delivery yields higher flexibility over traditional bulk optics, and a diffraction limited output, both of which are valuable properties in many applications, e.g., confocal and multiphoton microscopy. Additionally, an all-fiber delivery enables pulse delivery at places difficult to reach using conventional mirrors and lenses.
However, an all-fiber assembly for femtosecond laser pulses generally requires careful management of the dispersion and nonlinear properties of the fibers. One exemplary fiber type that is advantageous for ultrashort pulse applications is the air guiding hollow core photonic bandgap (PBG) fiber. The PBG fiber is known for its high nonlinear threshold, and at wavelengths around 800 nm and 1 μm, the dispersion of PBG fiber is anomalous, i.e. positive dispersion, which is significant factor for enabling fiber-based pulse compression of high energy ultrashort pulses.
One drawback associated with using PBG fibers for ultrashort pulse delivery has so far been limited to scientific demonstrations, although the fiber itself has been available several years. One reason for the lack of commercial availability of PBG fibers for such applications is a known problem with significant higher order dispersion, which cannot be eliminated by combination with standard single mode fibers. The dispersion slope of PBG fibers is typically large and positive, such that the relative dispersion slope (RDS), defined as dispersion slope divided by dispersion, becomes large and positive. Standard single mode fibers (SMF) have normal, i.e. negative, dispersion in the 800 nm and 1 μm range and a positive dispersion slope, and the RDS of SMF is therefore negative in the 800 nm and 1 μm range. The relative dispersion slope (RDS) between PBG fibers and SMF is opposite in sign such that there can be no RDS match between PBG fiber and SMF. As such, the practical use of the PBG fiber for pulse compression is currently limited to roughly greater than 200 fs, where its properties are acceptable.
Attempts of utilizing PBG fibers for shorter pulses have been made by combining the PBG fibers with a stretcher fiber, e.g., dispersion compensating stretcher fiber (DCF). While the attempted combination has showed some signs of success, there are still great limitations with respect to RDS matching between the two fibers, as well as overall power output of the fiber assembly since DCF's generally have low nonlinear threshold.
Thus, there is a need for an improved fiber assembly based on hollowcore PBG fibers for all-fiber delivery of high energy femtosecond pulses.